This Core provides an essential function for the overall scientific execution of the performance of the individual projects. A main purpose of the Animal Core is to maintain and insure the genetic integrity of the large number of unique genetically altered mouse lines available for the use of each member of the Program Project. Mice from each line will be maintained and genotyped by the Core and provided to the individual investigators for expansion as dictated by the experimental design. The duties of this core include responsibility for the breeding program, weaning pups and genotyping. Responsibility for adjusting the census of each mouse line in anticipation ofthe needs ofthe Pi's such that expansion ofthe individual lines can be accomplished to facilitate timely experiments. The core is also responsible for the generation of new transgenic lines required for the successful demonstration of the mechanisms underiying the hypotheses tested in each project. Lastly, the core is responsible for insuring the sterile maintenance of the bone marrow chimeric mice and the extent of chimerism prior to use by the individual projects.